I've been having electrical gremlins on my 2008 S2000 ever since I bought it. I'll summarize the symptoms and my failed attempts at fixing the issue.

1. It started out with slow cranking on start up. It had the 5 year old OEM battery so I figured it was time to replace it. While trying to decide which battery to buy, a few other anomalies happened.
2. Rolling the windows down simultaneously caused it to stall out once. I restarted it but couldn't reproduce the issue.
3. A couple of days later, putting the top down caused some warning lights to go on/off/on/off. I turned my wheel to leave the spot caused the steering the lock up and resist. As I did this, I noticed that my headlights were also flashing on and off. The CEL came on and stayed on. I turned off my car then back on. It resulted in no CEL and its back to normal. I was able to drive to O'Reilly's without issue. Being new to the s2k, I couldn't find the OBDII port..lol. The alternator tested fine. The battery had a weak cell. I went home without issue.
4. I parked it while I waited for my battery. I replaced it on Dec 2013. It lasted 5 months before issues started back up.
5. The VSA light and ! came on and stayed on. The next day, the lights were still on but turned off after a couple of miles. I checked fluid levels and the float. Normal for about a month.
6. I was leaving work and issue outlined on "3" happened again. Restarted the car, everything normal except for the whole dash looked like it was flickering.
7. I replaced the alternator with a reman Denso. No issues for 3 weeks.
8. Today, out on a cruise, I noticed that my VSA, Parking Brake, ABS, !, and EPS flashing on/off/on randomly for a split second. I made it back to work safely.
9. I parked the car and was able to recreate issue "3" by turning on the AC, Headlights and cranking the steering wheel left and right. I scanned the code and it came up with: P0685 ECM\PCM Power Real Control Circuit /Open.

I'm at a loss as to where to start. Has anyone ever experienced this issue? My research has led me to either: bad battery terminals, defective ECU, potential blown fuses. Any help would be appreciated.

 

I just got home from work and was unable to replicate the issue.

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Could be a faulty ECU or a poor ground or loose ground. Possibly a relay as well.

 

Thanks for the reply. That's where the CEL code lead me as well. I found this old thread and I pm'd the OP. The issue ended up being the alternator. I know I just replaced mine but it's possible that I could've gotten a bad one. I bought it from this seller on ebay.

I'm going to get the battery and alternator checked tomorrow. I still don't get why its not a consistent issue.

 

I found my multimeter last night and did some testing:
1. Car off: 12.5v
2. Car on idling with no accessories: 12.5 to 12.7v
4. Car on with AirCon (full), radio, defroster, low beams, hazards: 13.8v - 14 v
5. Multimeter in AC voltage mode: 0v

I could not replicate the issue no matter what I did.

This morning I decided to take it to Advance Auto. Both alternator and battery (optima yellow top) came back normal:



So..where should I start from here?

*found this on another forum. It's a good read: http://opensiuc.lib.siu.edu/cgi/view...text=auto_pres

 

I decided to go for another spirited drive (same route from yesterday but coming from the other direction) today and it was completely normal. I had my OBDLink app running on my phone to monitor the battery voltage. The data I gathered directly coincides with the article's "dual charging system".

Idle: 12.4v
Idle with AC ON: 14.0-14.4v
Engine load and AC on: 14.2-14.4v
Engine load (no accessories) @ 4k rpm and above: 14.4v
Engine load (no accessories) below 4k rpm: 12.6v

I drove about 30 miles in 1 hour.

 

The flashing malfunction indicator lamps (ABS, VSA, !, EPS, Parking Brake) happened on my short commute on the way back to work from lunch. The car drives normally other than the intermittent flashing of warning lights. I'll check my grounds and fuses tomorrow.

I'm guessing that based on the lack of response that no one's ever since this issue..?

 

Know any other s2k'ers around that would be willing to swap ECU for a week? Rather than wasting your time tracking the electrical fault(s), I would try this first. Might save you time in the long run.

Electrical issues are such a bitch because there are so many variables.

Do your issues arise only when you are drawing power. Such as, turning on A/C, headlights, radio, roof, etc.? Try to turn on all your accessories at the same time, while at idle and see if you get a stall.

 

Unfortunately, I don't know any other ap2s in the area. The electrical issue seems to be very intermittent. Once it starts happening I can make it worse by increasing load to the point of the CEL but as soon as I turn it off and leave it alone for a few, then back on, the issue disappears and no amount of fiddling will replicate what just happened.

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I had a breakthrough on this issue today. I decided to take to take it to O'Reilly's to get a second reading on my alternator. A friend of mine suggested I check the amp output to see if it matched spec (109amps). Why didn't I think of that? The car drove normally for the 10 minute drive with the AC on.

When I finally got a tech, we went outside and measured voltage on the battery: 12.9v. As soon as I started the car, I knew immediately that I got "lucky" in terms of recreating the issue. The dash lit (ABS, VSA, !, EPS, Parking Brake) briefly but turned over without issue and idled. Voltage kicked up to 14.4v as I started to turn accessories on. I turned my hazards on and bam!, the dash lit up again. The blower fan and engine idle started to pulsate in beat with the hazards. I had him measure the amps and it was reading less than 30 amps!.

I bought the reman from O'Reilly's -- Ultima alternator (which has a lifetime warranty). I'm getting it tomorrow and will mostly like install it after I get off of work. I'm waiting atleast a couple of days before I declare victory but I think I may have found the smoking gun. Thanks for the help s2ki.